The reaction of ozone with olefinically unsaturated organic compounds has been known for many years, and has been the subject of extensive study. Advances in ozonation chemistry are collected and reported in Chem. Revs., 27, 437 (1940); Chem. Revs., 45, 385 (1949); Chem. Revs., 58, 925 (1958); and "Ozonation in Organic Chemistry", P. S. Bailey, Volume 1, 1978 (Academic Press, N.Y.).
Typically, ozonation reactions are conducted by dissolving the olefin in a solvent and contacting this solution by suitable means with ozone or a mixture of ozone-containing gases at a temperature from about -100.degree. C. to about 30.degree. C. The ozonide thus produced is then further treated such as by oxidation to obtain acid products or by reduction if alcohol or aldehyde/ketone products are desired.
Many methods for the preparation of carboxylic acids by the ozonation of unsaturated organic compounds followed by oxidative decomposition of the ozonides are known. Besides oxygen, hydrogen peroxide has been used as oxidant, usually in formic or acetic acids. In these cases the actual oxidizing agent is probably performic or peracetic acid. Silver oxide suspended in sodium hydroxide, potassium permanganate, and chromic acid have also been employed. In order to merge the two reaction steps (ozonation and oxidation) into one, the ozonide or ozone-adduct is reacted immediately after its formation with an oxidizing component which preferably acts also as the reaction medium.
Many methods have been developed for preparing useful products from the ozonides, such as hydrogenation to convert them into alcohols, hydrolysis to convert them into a mixture of aldehydes and acids, oxidation to convert them into acids and the like. In all of the various methods difficulties are usually encountered in controlling the rate of the reaction and the composition of the resulting reaction product.
The ozonolysis of .alpha.,.beta.-unsaturated carbonyl compounds proceeds via an "abnormal" reaction mechanism, i.e., both the olefinic bond and the adjacent single bond connecting the carbonyl group are cleaved, as illustrated by Dauben et al in J. Org. Chem., 23, 1787 (1958): ##STR1##
Chavdarian et al in J. Org. Chem., 40, 2970 (1975) report the preparation of a compound such as 5-hydroxy-3,3-dimethylpentanoic acid delta-lactone by ozonation in methanol at -60.degree. C. followed by reduction with sodium borohydride: ##STR2##
Dauben et al J. Org. Chem., 30, 1693 (1965) report the ozonolysis of 6-isopropyl-3-methyl-2-cyclohexen-1-one to 2-isopropyl-5-oxohexanoic acid. The procedure involves ozonation in methanol followed by reflux with excess 30 percent hydrogen peroxide: ##STR3##
The use of an oxidant such as hydrogen peroxide to convert an ozonide intermediate into carboxylic acid products inherently has several disadvantages. The oxidation reaction is nonselective and tends to attack all oxidizable functionality in the molecules and thereby lowers the yield of desired product. Further, it is necessary to employ a large quantity of a reducing agent such as sodium sulfite to eliminate the excess oxidizing agent at the end of the reaction.
W. Carruthers, "Some Modern Methods of Organic Synthesis", 279, 1971 (Cambridge University Press) also describes the ozonolysis of an .alpha.,.beta.-unsaturated ketone into a keto-acid, wherein the ozonation is performed in acetic acid followed by reflux with excess hydrogen peroxide.
Accordingly, it is an object of this invention to provide an improved process for converting an .alpha.,.beta.-olefinically unsaturated ketone compound to a carboxylic acid product.
It is another object of this invention provide a convenient and efficient method of ozonating an alicyclic .alpha.,.beta.-olefinically unsaturated ketone compound to an oxocarboxylic acid product which contains at least one less carbon atom per molecule than does the ketone starting material.
It is a further object of this invention to provide a process for ozonating an alicyclic .alpha.,.beta.-unsaturated ketone compound to an oxocarboxylic acid product, without the need to treat the ozonide intermediate with a secondary oxidizing agent.
Other objects and advantages of the present invention shall become apparent from the accompanying description and Examples